1. Field of the Invention
The present invention relates to a flow sensor, a method for manufacturing a flow sensor and a flow sensor module, comprising a semiconductor device having a flow sensing unit for sensing flow of air or other fluids and a diaphragm formed thereto, and a board or a lead frame having an electric control circuit for controlling the semiconductor device disposed thereto, wherein a surface of the electric control circuit and a part of a surface of the semiconductor device is covered with resin while the air flow sensing unit portion of the semiconductor device is exposed.
2. Description of the Related Art
In a conventional flow sensor composed of a semiconductor device equipped with an air flow sensing unit, an electric control circuit and a board, gold wires electrically connecting the semiconductor device and the board are protected and fixed via a potting resin. The fixing using the potting resin is normally performed without clamping the semiconductor device via molds or the like, so that the shrinkage of the potting resin may cause the semiconductor device to be displaced. Therefore, the fixing performed via the potting resin has a drawback in that the dimensional accuracy of the semiconductor device may be deteriorated. Further, since a relatively long time is required for curing the potting resin, the manufacturing costs become high.
This problem can be solved by providing a structure that molds and fixes the semiconductor device including the air flow sensing unit to the board or the lead frame with the air flow sensing unit portion exposed, instead of performing potting as in the prior art.
At this time, molding can be performed while clamping the semiconductor device via the mold so as to improve the positioning accuracy of the semiconductor device and the board after molding and to shorten the resin curing time by the heat transfer from the mold to the resin.
Patent documents 1 and 2 disclose known mold integrated structures in which the semiconductor device including the air flow sensing unit and the lead frame are molded integrally.
Patent document 1 (Japanese patent application laid-open publication No. 11-006752, Japanese patent application No. 9-158739) and patent document 2 (Japanese patent application laid-open publication No. 2008-111668, Japanese patent application No. 2006-293030) disclose a structure in which one end of a semiconductor sensor device not having a cavity section or a heating resistor is integrally molded with a lead frame.
According to the structure disclosed in patent documents 1 and 2, the area of a surface of the semiconductor device other than the air flow sensing unit is not surrounded via resin or a lead frame, so that the structure has a drawback in that the flow of air on the air flow sensing unit side cannot be detected accurately since air flows into the diaphragm having a narrow passage.
Furthermore, upon manufacturing the structure disclosed in patent documents 1 and 2, during the process for placing the semiconductor device and the lead frame in a mold and integrally molding the same via resin, the semiconductor device and the lead frame must be clamped and fixed via the mold to prevent flash and to determine the position of the semiconductor device.
The structural drawback of patent documents 1 and 2 according to this manufacturing process is that when the semiconductor device is clamped via the mold, the dimensional variation of the semiconductor device or the adhesive for bonding the semiconductor device to the lead frame may cause flash or chip crack of the air flow sensing unit on the semiconductor device when the device is clamped via the mold.
The present invention aims at solving the problems mentioned above by providing a flow sensor structure in which surfaces of a resin mold, a board or a pre-mold component molded in advance surround the semiconductor device in such a manner that they are not in continuous contact with three walls of the semiconductor device orthogonal to a side on which the air flow sensing unit portion is disposed on the semiconductor device.
The present invention further provides a manufacturing method capable of absorbing the dimensional variation of the semiconductor device via the deformation of springs or deformation of an elastic film in the thickness direction by supporting an insert of a mold clamping the semiconductor device via springs or by disposing an elastic film on the surface of the mold. In other words, the present invention enables to prevent the occurrence of flash or chip crack even when the dimension of the semiconductor device is varied.
According to the conventional flow sensor, the gold wires electrically connecting the semiconductor device and the board are protected and fixed via potting resin. The fixture using potting resin is performed without clamping the semiconductor device via the mold or the like, so that the shrinkage of the potting resin may cause the semiconductor device to be displaced. Therefore, the fixture using potting resin not only deteriorates dimensional accuracy but also requires a long time for curing the potting resin, so that the costs related thereto become high.
The present problem can be solved by adopting a structure to fix the semiconductor device having the air flow sensing unit to the board or the lead frame via molding while having the air flow sensing unit exposed, instead of performing the prior art potting.
The problem of the structure for fixing the components via molding is to prevent air from flowing into the diaphragm portion having a narrow passage. The present invention provides a flow sensor structure in which the walls composed of a resin mold or a board or a pre-mold component molded in advance surrounds the semiconductor device without being in continuous contact with three walls of the semiconductor device orthogonal to a side of the semiconductor device on which the air flow sensing unit is disposed.
The problem to be solved related to the manufacturing method of the flow sensor is to prevent the occurrence of flash or chip crack of the semiconductor device when the device is clamped via the mold.